The present invention relates to deflecting the flow direction of a primary fluid, and more particularly to apparatus and method whereby a secondary fluid is injected into the primary fluid stream to change the direction of flow of the primary fluid stream.
Thrust vectored aircraft have many advantages over aircraft using conventional aerodynamic control surfaces. They can lead to tactical advantages in the aircraft""s agility and maneuverability and also to improved take-off and landing performance, e.g. on battle-damaged runways or aircraft carriers. Thrust vectored aircraft can also operate outside of the conventional flight envelope, i.e., in the post-stall regime thus giving the pilot a significant advantage leading to improved survivability.
Designing aircraft without tails offers the potential for reduced weight and increased performance, efficiency and stealth. Aircraft such as the X-31 have demonstrated flight without a tail through a supersonic in-flight experiment in which the flight control system reacted as though the aircraft had no tail. The thrust vectoring capability was used to provide necessary aircraft stability, trim and control.
Most of the research in this field has been directed at designing and developing mechanically based systems. Although these systems are effective and may also lead to the removal of conventional moving surfaces and hence to a reduction in drag, they carry many disadvantages. For example, they often involve the use of complex mechanical actuation systems. They are also usually very expensive, difficult to integrate and aerodynamically inefficient. Further, as stealth requirements become ever more important, the radar cross section (RCS) and infra-red radiation (IR) signatures of military aircraft must be minimized.
One alternative to mechanical systems is known as fluidic thrust vectoring, which uses a secondary fluid stream to change the vector angle of a primary exhaust fluid stream from an engine nozzle, thus leading to a change in the overall orientation of the aircraft. Fluidic thrust vectoring involves no external moving parts thus leading to a decrease in radar cross section and infrared signature. Additionally it is lightweight, inexpensive, and easy to implement.
Extensive research of different nozzle shapes and aspect ratios has previously been conducted in connection with future aircraft configurations. Some of the prior innovations focus on the integration and aerodynamic efficiency of the exhaust system. Other innovations focus on mechanical configurations that are intended to effect thrust vectoring. Still other innovations have incorporated fluidic principles with the objectives of generating thrust vectoring power or controlling the effective flow area of a nozzle.
For example, U.S. Pat. No. 5,996,936 to Mueller discloses an exhaust nozzle for a gas turbine engine which includes a converging inlet duct in flow communication with a diverging outlet duct at a throat therebetween. Compressed air from the engine is selectively injected through a slot at the throat for fluidically varying flow area at the throat.
U.S. Pat. No. 6,112,512 to Miller et al. discloses an apparatus and method for varying the effective cross sectional area of an opening through a fixed geometry nozzle to provide a fluidic cross flow with an injector incorporated in the throat of the nozzle proximate to the subsonic portion of the flow through the nozzle. One or more injectors are directed at an angle in opposition to the subsonic portion of the flow. The opposed cross flow from the injectors interacts with a primary flow through the nozzle to partially block the nozzle""s opening, thereby effectively decreasing the cross sectional area of the nozzle throat. A plurality of cross flows proximate to a nozzle""s throat permits effective afterburner operations even with a fixed geometry nozzle by allowing throttling of the primary flow. Further, variations in the cross flow""s mass flow characteristics or injection angle can allow vectoring of the primary flow.
U.S. Pat. No. 4,018,384 to Fitzgerald et al. teaches deflection of only a portion of the fluid thrust emanating from a nozzle, but the deflection takes place as a result of mechanical devices rather than another fluid stream. U.S. Pat. No. 4,686,824 to Dunaway et al. discloses apparatus for modulating the thrust vector of a rocket motor by injecting gas into the divergent section of the rocket nozzle and modulating injection of the hot gas by varying the flow from a solid propellant gas generator by controlling its flow rate with a vortex throttling valve arrangement. And U.S. Pat. No. 5,694,766 to Smereczniak et al. discloses a method and apparatus for controlling the throat area, expansion ratio and thrust vector of an aircraft turbine engine exhaust nozzle, using means, such as deflectors and/or injected air, for producing and controlling regions of locally separated flow, as well as control of the thrust vector angle defined by the gas exiting the nozzle to provide increased directional control of the aircraft.
The nozzle shapes studied in the patents mentioned above tend to be circular or of low aspect ratio. Fluidic injection from the top, bottom, and sidewall surfaces of nozzles and combinations of the three have also been analyzed, but have failed to produce the high levels of thrust vectoring and aerodynamic performance thought to be needed for quick maneuverability and efficient performance. Until recently, the amount of thrust vector angle generated with fluidics has not been high, typically less than eight degrees, and therefore, thrust vectoring through fluidics alone has only been found to be applicable to a very limited range of vehicle designs. Moreover, the efficiency of prior nozzle designs which used fluid injection or secondary flow to generate thrust vectoring has been quite low, typically on the order of 1.6 degrees of vector angle or less per each percent of secondary flow F2 extracted from the primary flow F1 at a primary nozzle pressure equal to 4 times the free-stream static pressure (Nozzle Pressure Ratio (NPR)). Thus, since it typically is not desirable to extract more than 10 percent of the primary flow to provide secondary flow, peak thrust vector angles have been low while inefficiently utilizing high secondary flow rates in nozzle shapes that are limited in their applicability to advanced designs and requirements.
It is therefore desirable to provide increased fluidic thrust vectoring capability to enhance vehicle maneuverability, as well as decrease radar and infrared cross section, and minimize requirements for additional moving parts, thereby improving reliability while reducing weight, cost, and complexity.
Against this background of known technology, an apparatus to develop relatively high thrust vectoring power and efficiency in a broad range of configurations is provided. Some embodiments of such an apparatus include a nozzle with one or more injectors that introduce a secondary fluid against the direction of flow of a primary thrust fluid, thereby providing an apparatus with high thrust vectoring capability that can be easily integrated into a wide variety of vehicle configurations. The thrust vectoring nozzle can exert forces in one or more directions simultaneously to maneuver and control the vehicle about one or more axes of movement including pitch, roll and/or yaw.
In one embodiment, the injector(s) are formed in the sidewalls of the nozzle by drilling or otherwise forming a hole at an angle relative to the surface of the sidewall. A plenum is attached to one side of the nozzle sidewall to deliver the secondary fluid to the injector(s). Any number, size, and configuration of injectors can be disposed in each sidewall to provide the desired amount of maneuvering control. In general, the injectors can be disposed at any position, but are typically positioned as close to the exit area of the primary flow as possible.
A controller can be included to regulate the amount and duration of secondary flow delivered. The controller can be coupled to regulate the secondary flow to one or more plenums simultaneously. An operator or an autonomous control system can provide attitude or attitude rate commands, which are translated to secondary flow injections by the controller. Attitude and attitude rate feedback can be provided to the controller to allow the controller to refine the amount of secondary flow injected over time.
A variety of nozzle shapes and sizes can be configured to accommodate the injectors in their sidewalls, including high aspect ratio nozzles capable of generating thrust vectoring capability beyond that available in the prior art.
The secondary fluid can be provided by extracting some of the primary fluid, or by providing an independent source of secondary fluid.
While various configurations of the nozzles can be utilized in air vehicles, it is expected that embodiments of a device for altering the direction of flow of a primary fluid using secondary fluid injection can be utilized in other types of vehicles as well. The primary and secondary fluids can be in gaseous, solid particle, or liquid form. Other advantages and features of the invention will become more apparent, as will equivalent structures which are intended to be covered herein, with the teaching of the principles of embodiments of the present invention as disclosed in the following description, claims, and drawings.